[Bug 1876506] Re: eoan to focal upgrade hangs when lvm snapshot is present

[Julian Andres Klode]

bug 1887373 suggests it is hanging in memtest86+ postinst

** Package changed: os-prober (Ubuntu) => memtest86+ (Ubuntu)

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Title:
  eoan to focal upgrade hangs when lvm snapshot is present

Status in memtest86+ package in Ubuntu:
  Confirmed
Status in memtest86+ source package in Focal:
  Confirmed

Bug description:
  When upgrading from 19.10 (w/ LVM + encypted disks) to 20.04, the
  installer hangs when trying to probe an LVM snapshot volume created
  before the upgrade.

  Steps to reproduce:

  lvcreate -s -L 20G -n preupgrade /dev/vgubuntu/root 
  do-release-upgrade -d

  The installer will hang after the following message:

  /usr/sbin/grub-probe: error: unknown filesystem.
  Found Ubuntu 19.10 (19.10) on /dev/mapper/vgubuntu-preupgrade
  done

  Resolution:

  Killing the grub-mount process which is probing the LVM snapshot seems
  to unhang the installer and allow the upgrade to complete without
  issue.

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